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Diffstat (limited to 'doc/tell.n')
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diff --git a/doc/tell.n b/doc/tell.n new file mode 100644 index 0000000..e8bf3af --- /dev/null +++ b/doc/tell.n @@ -0,0 +1,48 @@ +'\" +'\" Copyright (c) 1993 The Regents of the University of California. +'\" Copyright (c) 1994-1996 Sun Microsystems, Inc. +'\" +'\" See the file "license.terms" for information on usage and redistribution +'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. +'\" +.TH tell n 8.1 Tcl "Tcl Built-In Commands" +.so man.macros +.BS +'\" Note: do not modify the .SH NAME line immediately below! +.SH NAME +tell \- Return current access position for an open channel +.SH SYNOPSIS +\fBtell \fIchannelId\fR +.BE +.SH DESCRIPTION +.PP +Returns an integer string giving the current access position in +\fIchannelId\fR. This value returned is a byte offset that can be passed to +\fBseek\fR in order to set the channel to a particular position. Note +that this value is in terms of bytes, not characters like \fBread\fR. +The value returned is -1 for channels that do not support +seeking. +.PP +\fIChannelId\fR must be an identifier for an open channel such as a +Tcl standard channel (\fBstdin\fR, \fBstdout\fR, or \fBstderr\fR), +the return value from an invocation of \fBopen\fR or \fBsocket\fR, or +the result of a channel creation command provided by a Tcl extension. +.SH EXAMPLE +.PP +Read a line from a file channel only if it starts with \fBfoobar\fR: +.PP +.CS +# Save the offset in case we need to undo the read... +set offset [\fBtell\fR $chan] +if {[read $chan 6] eq "foobar"} { + gets $chan line +} else { + set line {} + # Undo the read... + seek $chan $offset +} +.CE +.SH "SEE ALSO" +file(n), open(n), close(n), gets(n), seek(n), Tcl_StandardChannels(3) +.SH KEYWORDS +access position, channel, seeking |